CARBON FLUXES IN A MANAGED PINE FOREST UNDER AMBIENT AND ELEVATED CO{sub 2}

The primary objective of this study is to estimate CO{sub 2} fluxes (F{sub CO{sub 2}}) under ambient and elevated atmospheric CO{sub 2}, and varying environmental conditions. Additional objectives are to: (2) quantify canopy conductance and evaluate the hypothesis that canopy conductance will not be altered by elevated atmospheric CO{sub 2} because reduction in leaf conductance is compensated by increased leaf area index, and (3) quantify the effect of elevated CO{sub 2} on aboveground production and apparent allocation of carbon below ground. In order to achieve the primary objective, the authors propose a modification to a methodology proposed earlier which emphasized leaf level measurements. These modifications stem from analysis of measurements performed in 1995--1996 that demonstrate (i) high variability in CO{sub 2} assimilation (A)--internal concentration (C{sub i} relations A-C{sub i} curves) in each level in the canopy for given photosynthetically active radiation (PAR) and soil moisture content ({theta}) conditions, (ii) the relative independence of the ratio of C{sub i} to atmospheric CO{sub 2} concentration (C{sub i}/C{sub a}) from C{sub a} (different levels within canopy for a wide range of moisture content conditions), (iii) similarity in CO{sub 2} and water vapor flux co-spectra which permits estimation of CO{sub 2} conductances from water vapor conductances for canopy trees, and (iv) the good correlation (r=0.94) between scaled 15-tree stem flux measurements and eddy correlation water vapor flux on a daily time step